In a wireless communication system which performs communication using wireless terminals such as mobile phones and smartphones, remote base station equipment has been developed. Regarding this technique, NPL 1 discloses radio base station equipment for a remote LTE (Long Term Evolution) system. In NPL 1, radio BDE (Base Station Digital Processing Equipment) located on the side of the center (for example, a core network) and a plurality of pieces of RRE (Remote Radio Equipment) located near antennas are connected to each other via optical fibers using the CPRI (Common Public Radio Interface) scheme.
CPRI refers herein to an open specification of an interface between a wireless control unit (REC: Radio Equipment Control) and a wireless unit (RE: Radio Equipment) in a radio base station and is described in detail in NPL 2. NPL 3 discloses a C-RAN (Radio Access Network). The C-RAN is formed by connecting a DU (Digital Unit) cloud located on the side of the center (for example, a core network) to an RU (Radio Unit) distributed for each antenna site via a wideband, low-latency transport network. NPL 4 discloses the specifications of an E-UTRAN (Evolved Universal Terrestrial Radio Access Network) used in LTE.
In NPL 1, the pieces of RRE (Remote Radio Equipment) simply execute optical/electrical conversion and RF (Radio Frequency) functions and the BDE executes other digital signal processing functions (error correction coding, radio framing, data modulation, frequency/time conversion, and MIMO (Multiple Input Multiple Output) processing). NPL 2 also discloses a configuration obtained by similar function sharing.
PTL 1 discloses a digital fiber wireless transmission system which assumes a network architecture connecting a slave station to a radio base station (master station) over a cable extending from the master station, and includes a master device connected to a mobile communication network, one or more slave station devices capable of radio communication with a mobile communication terminal, and a transmission line connected between the master device and each slave device and capable of bidirectional digital transmission. Note that in PTL 1, a signal processing circuit in the master device processes main signals (included in transmission frames) communicated between the signal processing circuit and the slave device connected to a transmission control circuit, directly as digital signals by signal processing such as signal demodulation, encoding/decoding, error detection/correction, and channel termination/multiple separation according to the radio scheme and protocol used.